LF: Re: Alpha benchmark

["James Moritz" <james.moritz@btopenworld.com>]

Dear Mal, LF Group,

What you suggest might be useful as a benchmark for Alpha beacon reception, 
but not so helpful for 9kHz reception. The problem is that the relative 
noise level often varies a great deal between 9kHz and 11.9kHz, so you could 
have good Alpha reception and poor 9kHz reception, or vice versa.
Where Alpha beacon reception tests could be useful is for assesing receiver 
frequency stability - remembering that accuracy and stability of the order 
of milli-hertz or better is *essential* for 8.97kHz amateur tests. 
Monitoring the Alphas using spectrogram settings for DFCW-600 or slower over 
a period of at least several hours or preferably days is a simple way of 
assesing receiver drift at these levels. You can see examples at DF6NM's and 
DK7FC's VLF grabber pages.
For assesing receive system sensitivity, and local noise levels, you really 
have to do it at 8.97kHz directly. A quick check is to generate a 
spectrogram using QRSS3 settings - the display should be dominated by QRN, 
which should totally mask any receiver noise. Usually there will also be at 
least a few spectral lines from man-made sources present, especially 
harmonics of 50Hz, but many others can be present too. At my QTH, levels of 
this man-made noise vary greatly from one day to the next, as does the QRN.
Cheers, Jim Moritz
73 de M0BMU